The present invention relates to the general field of highway guardrail systems and roadside safety barriers. Principally, the invention is of an improved highway guardrail end treatment for guardrail barrier systems.
Highway safety devices utilized along most roadways are comprised primarily of guardrail barrier systems. Guardrails called W-beam guardrails are used to prevent vehicles from leaving the roadway and possibly colliding with fixed objects, other vehicles, or other safety hazards. For this, the semi-rigid guardrail barrier must be able to resist lateral impact forces, for instance a vehicle approaching at an angle to the length of rail. In this the barrier should perform in such a way that the vehicle is safely redirected back onto the roadway as opposed to tearing through or passing through the guardrail.
The ability of guardrail to resist this lateral loading force is dependent upon a universally accepted corrugated shape, which dissipates the energy of the vehicle in a safe and controlled manner. However, the rigidity of a W-beam guardrail is such that an upstream, or terminal end of a length of guardrail, can, in itself, present a hazard. Vehicles impacting the end section of a guardrail barrier without an appropriate terminal device encounter extreme forces that can lead to serious injury or death of the occupants. This problem of addressing terminal safety is a major area of research within the highway safety industry.
Recent design alternatives have placed emphasis on two main categories of terminal devices. These are terminal devices (or terminals) which gate the vehicle into a clear zone located behind the guardrail length opposite the roadway, and those that absorb the energy of the impacting vehicle through controlled dynamic buckling of the guardrail. Additionally, terminals can be either flared or tangent to the roadway.
Of the current terminal designs available, two are found to be the most widely used. Both systems are designed within the constraints of the currently accepted uniform standards, such that vehicles impacting at an angle to the length of guardrail are redirected away from the hazard. Functions during end-on impacts are design dependent to each terminal.
The first terminal system is an energy absorbing safety treatment which utilizes a customized head assembly. This head assembly functions to induce controlled buckling of the terminal guardrail, such that the vehicle is brought to a controlled stop after all impacting energy has been dissipated. The concept of this terminal system has been applied to both flared and tangent applications.
The second terminal system, existing only as a flared gating system, utilizes slotted regions in the W-beam guardrail to reduce column strength in longitudinal impacts. A designed plate is set to maintain structural integrity during impacts, such that said slotted regions do not tear and allow the vehicle to pass through the barrier.
Therefore, the intent of highway safety is to develop guardrail terminal systems which will address the issue of end-on impacts, and at the same time maintain adequate structural integrity to safely redirect vehicles during lateral impacts. Alternative designs to existing systems should provide equivalent or better safety performance, as well as increase the availability of safety hardware through lowered costs, easier installation, and wide availability of common parts.